Hearing "number"? Relative quantity judgments through the echolocation by bottlenose dolphins (Tursiops truncatus)

Area of Science:

• Marine Mammal Cognition
• Sensory Biology
• Acoustic Perception

Background:

• Dolphins utilize echolocation for environmental perception, discerning object properties like shape and size.
• Limited research exists on dolphin echolocation for quantity discrimination beyond size and thickness.
• The applicability of Weber's law to echolocation-based quantity judgments in dolphins is not well understood.

Purpose of the Study:

• To investigate bottlenose dolphins' ability to discriminate relative quantities of underwater objects via echolocation.
• To determine if Weber's law applies to echolocation-based numerical discrimination in dolphins.
• To compare echolocation-based quantity judgments with visual discrimination abilities.

Main Methods:

• Bottlenose dolphins were presented with visually occluded objects underwater.
• Dolphins performed relative quantity judgments on pairs of objects ranging from one to eight.
• Object number discrimination was tested under congruent and incongruent conditions with object size.

Main Results:

• Dolphins successfully discriminated object numbers (1-8) using echolocation.
• Discrimination accuracy improved with increased numerical difference ratios and larger quantities.
• Echolocation discrimination accuracy was comparable to visual judgments.
• Performance decreased when object size was incongruent with number, but number ratio effects persisted.

Conclusions:

• Bottlenose dolphins demonstrate echolocation-based numerical discrimination abilities.
• Dolphin performance suggests adherence to Weber's law principles in quantity judgments.
• Dolphins flexibly integrate multiple sensory cues (number and size) for quantity assessment.
• Echolocation provides a robust sensory channel for complex quantitative information processing in dolphins.